Good-Case and Bad-Case Latency of Unauthenticated Byzantine Broadcast: A Complete Categorization

Authors Ittai Abraham, Ling Ren, Zhuolun Xiang

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Author Details

Ittai Abraham
  • VMware Research, Herzliya, Israel
Ling Ren
  • University of Illinois at Urbana-Champaign, IL, USA
Zhuolun Xiang
  • University of Illinois at Urbana-Champaign, IL, USA


The authors would like to thank Kartik Nayak for helpful discussions related to the paper.

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Ittai Abraham, Ling Ren, and Zhuolun Xiang. Good-Case and Bad-Case Latency of Unauthenticated Byzantine Broadcast: A Complete Categorization. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 5:1-5:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


This paper studies the good-case latency of unauthenticated Byzantine fault-tolerant broadcast, which measures the time it takes for all non-faulty parties to commit given a non-faulty broadcaster. For both asynchrony and synchrony, we show that n ≥ 4f is the tight resilience threshold that separates good-case 2 rounds and 3 rounds. For asynchronous Byzantine reliable broadcast (BRB), we also investigate the bad-case latency for all non-faulty parties to commit when the broadcaster is faulty but some non-faulty party commits. We provide matching upper and lower bounds on the resilience threshold of bad-case latency for BRB protocols with optimal good-case latency of 2 rounds. In particular, we show 2 impossibility results and propose 4 asynchronous BRB protocols.

Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed algorithms
  • Security and privacy → Distributed systems security
  • Byzantine broadcast
  • asynchrony
  • synchrony
  • latency
  • good-case
  • optimal


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